In order to stack IC die in a face-to-face manner using standard flip-chip assembly techniques, the assembly is conventionally performed in a sequential manner by bonding a first thinned IC die then a second thinned IC die (e.g., 25 to 150 μm) onto a package substrate (e.g., PCB). In a typical arrangement, the first IC die can be a TSV comprising die that is mounted face (i.e. active circuit side) up on the surface of a package substrate where the TSVs form joints with pads on the package substrate surface. Capillary underfill is then generally performed. The second IC die is then generally flip-chip mounted to the active circuit side of the first IC die.
Problems with this conventional sequential stacked die assembly technique include a complicated process flow. There are also difficulties with die-to die jointing via bumps because the first IC die mounted that is on the package substrate may have significant warpage/bow. In addition, since both IC die are thinned and the top active circuit comprising sides are exposed during assembly, die handling is generally difficult and can result in yield loss due to cracked IC die or scratching of the IC die.